Device for measuring and correcting the luminance of a display

ABSTRACT

A flat screen panel arrangement is proposed, which can be illuminated from the rear by the light of a backlight, having a backlight control, which adjusts a luminance measured by a sensor to a selectable setpoint value representing the intensity of the light of the backlight. The sensor is arranged in an area of the flat screen that is not visible to a viewer, and means are provided to swivel the sensor out, essentially parallel to the panel, from a standby position to a position for measuring the luminance of a test image that can be displayed on the panel during a calibration phase. As a result, effects due to aging and/or temperature of the panel and interfering with the luminance of the panel are detected and can be largely corrected.

The invention relates to an arrangement with a flat screen panel, which can be illuminated from the rear by means of a backlight, having a backlight control to adjust a luminance measured by a sensor to a selectable setpoint value, which represents the intensity of the backlight.

To control the luminance of the backlight for a so-called LCD panel (flat screen LCD display), a backlight control is usually provided. This backlight control adjusts the luminance of the backlight illuminating the panel from the rear and measured by a sensor to an essentially constant setpoint value. The drawback is that such a control measures and regulates only the luminance of the backlight, while influences affecting the luminance of an image displayed on the panel are not measured and can therefore not be corrected. For example, it is not possible to measure and correspondingly correct effects that interfere with the luminance of the image due to aging of the glass, the LCD fluid or the diffuser and/or polarization foils of the panel.

The German application with the official file number 10323221.4 proposes to arrange transparent parts between a sensor and a backlight whose aging and temperature properties essentially correspond to those of the transparent parts of the panel. The sensor measures the luminance of these transparent parts, which a backlight control adjusts to a selectable setpoint value, such that effects due to aging and/or temperature of the panel that interfere with the luminance of an image displayed on a flat screen panel are largely avoided. The drawback is that, for example, the temperature influences within and outside the flat screen differ, so that the luminance can be detected only imprecisely.

The object of the present invention is to provide an arrangement of the initially described type, which makes it possible to measure and largely correct effects due to aging and/or temperature of the panel, which interfere with the luminance of the panel.

This object is attained by arranging the sensor in an area of the flat screen that is not visible to a viewer and by providing means to move the sensor essentially parallel to the panel from a standby position to a position for measuring the luminance of a test image that can be displayed on the panel.

This has the advantage that on the one hand effects interfering with the luminance of an image due to aging of the transparent parts of the panel, e.g., aging of the panel glass, the LCD fluid or the diffuser and/or polarization foils, are reduced and on the other hand the sensor is visible above the display surface only during a calibration phase. The invention makes it possible, in particular, to meet the requirements in the medical field in view of prescribed calibration cycles for adjusting the luminance of an image. At intervals of, for example, three months, the luminances of a test image are measured and are taken into account when the backlight is adjusted for a subsequent period.

One embodiment of the invention provides that the sensor can be lowered toward the panel to reduce the distance between the sensor and the panel to obtain better measurement results.

The measurement results are further improved by providing sealing means to shield the sensor from ambient light. These sealing means, e.g., in the form of sealing lips, prevent the ambient light from affecting the measurement results.

In a further embodiment of the invention, according to the measures described in Claim 4, the sensor is automatically cleaned. As a result, contamination of the sensor that would affect the measurement results is largely avoided and sensor maintenance intervals can moreover be increased.

Advantageously the sensor and the means for swiveling the sensor out are arranged in a recess of the frame, preferably the lateral frame of the flat screen. As a result, the sensor and the swiveling means are not visible to a viewer during normal operation, i.e., outside the calibration phases.

The invention, its embodiments and advantages will now be described in greater detail with reference to an exemplary embodiment of the invention depicted in the drawing, in which:

FIG. 1 shows an arrangement for adjusting the luminance of a backlight for an LCD panel, and

FIGS. 2 and 3 show a sensor arranged on a sensor holder in a front view, a side view and a top view.

In FIG. 1, 1 identifies a graphics processor, which can be supplied with digitized image information (not depicted) for display on an LCD panel 3 of a flat screen. The graphics processor 1 transmits a selectable setpoint value Sw to the backlight control 2. The backlight control adjusts the luminance of the panel 3 substantially constantly to a desired luminance that corresponds to the setpoint value Sw. In a factory setting, the setpoint value Sw is defined such that the luminance of an image that can be displayed on the panel 3 imparts an optimal impression of the image. To adjust the luminance, a backlight sensor Bs is provided to measure the light from a backlight 6, which illuminates the panel 3 from the rear and the light intensity of which effects a corresponding luminance on the panel 3. The backlight sensor Bs feeds an actual value Iw corresponding to this luminance of the backlight 6 to the backlight control 2, which adjusts this actual value Iw to the setpoint value Sw.

When the flat screen is used, for example, in the medical field, it may occur that, e.g., aging and/or temperature or other environmental influences, have a negative effect on the luminance of the panel 3. To largely prevent these influences, the invention provides that during a calibration phase, a measuring unit on the front of the panel 3 scans the optical image information of a test image displayed on the panel, e.g., a white test image, and thereby measures the luminance of this test image. The measuring unit feeds a correction luminance value Kw corresponding to this luminance to the backlight control 2. The test image does not need to fill the panel completely. It is sufficient to display the test image in a “calibration window,” such that the test image can be overlaid in this window even while an image is being displayed in a normal operating phase of the flat screen. Components of the measuring unit are a sensor 4 and a sensor holder 5 on which the sensor 4 is mounted. The sensor 4 and sensor holder 5 are arranged in a recess in the frame of the flat screen so that they are not visible to a viewer. To be able to measure the luminance of the test image during the calibration phase, the sensor 4 can be swiveled out from a standby position to a detection position essentially parallel to the panel in which the sensor 4 is visible to the viewer. The sensor 4 is preferably lowered toward the panel 3 as it is swiveled out such that the sensor 4 can readily measure the luminance without touching the panel 3. After the calibration phase, the sensor 4 is swiveled back into its standby position in which the sensor 4 and the sensor holder 5 are again positioned in the recess of the flat screen so that they are not visible to the viewer.

The backlight control 2 uses the luminance correction value Kw to adjust the actual value Iw to largely eliminate effects 3 due to aging and/or temperature or other environmental influences on the luminance of the panel. The correction value Kw changes the deviation between the setpoint value and the actual value, which is evaluated by a control algorithm of the backlight control 2. The automatic control is effected by a corresponding adjustment of the light of a backlight 6, which illuminates the panel 3 from the rear and the light intensity of which causes a corresponding luminance on the panel.

To prevent ambient light from interfering with the measurement of the luminance, sealing lips (not depicted) are provided, which shield the sensor 4 from the ambient light.

Reference is now made to FIGS. 2 and 3, which depict a sensor 8 arranged on a sensor holder 7 in a front view (FIGS. 2 a, 3 a), a side view (FIGS. 2 b, 3 b) and a top view (FIGS. 2 c, 3 c). The sensor holder 7 is rotatable and can be pivoted by an actuator 9 and mechanical means 10. The actuator 9, e.g., an actuator made by NanoMuscle (Internet address: http.nanomuscle.com), together with the sensor holder 7 and the sensor 8, is arranged in a recess of a frame of a flat screen, preferably on a vertical portion of the frame, and is mounted on a base plate 11, which is arranged parallel to the frame and is covered by the frame. Thus, in a standby position (FIG. 2) the base plate 11, the mechanical means 10, the actuator 9, the sensor 8 and the sensor holder 7 are not visible to a person looking at the panel. In a measurement position during a calibration phase (FIG. 3), in which the sensor 8 measures the luminance of a panel, the sensor holder 7 with the sensor 8 is swiveled by 90°. During the swivel process, the sensor holder 7 is simultaneously lowered toward the panel surface (indicated in FIGS. 3 b, 3 c by the lowering height H) to position the sensor 8 closer to the panel surface. Sealing lips (not depicted) prevent the ambient light from distorting the measurement results. Once the sensor 8 has been positioned, it measures the luminance of the test image displayed on the panel in a calibration window for the duration of the calibration phase. The calibration window can be overlaid onto the normal image. After the calibration phase, the sensor 7 is swiveled back into its standby position. 

1-5. (canceled)
 6. A display device comprising: a display panel for a flat screen, which is illuminated from the rear by light from a backlight; a sensor, which measures luminance; a backlight control, which adjusts the light intensity of the backlight to a selected setpoint value based on the luminance measured by the sensor; and a swivel means for swiveling the sensor; wherein, in a standby position, the sensor is arranged in an area of the display device that is not visible to a viewer; and wherein the swivel means swivels out the sensor, substantially parallel to the display panel, during a calibration phase, from the standby position to a measurement position, for measuring the luminance of a test image that is displayed on the display panel.
 7. A display device as claimed in claim 6, wherein the swivel means lowers the sensor toward the display panel when the sensor is swiveled out.
 8. A display device as claimed in claim 6, further comprising a shielding means for shielding the sensor from ambient light while the luminance is being measured.
 9. A display device as claimed in claim 8, wherein the shielding means comprises sealing lips.
 10. A display device as claimed in claim 6, further comprising a cleaning means for cleaning the sensor while the sensor is swiveled out into the measurement position.
 11. A display device as claimed in claim 6, wherein the sensor and the swiveling means are arranged in a recess of a frame of the flat screen.
 12. A display device as claimed in claim 6, further comprising a cleaning means for cleaning the sensor while the sensor is swiveled back into the standby position.
 13. A display device as claimed in claim 6, wherein the test image is displayed in a window on the display panel which is smaller in size than the display panel.
 14. A display device as claimed in claim 6, wherein the test image is displayed in a window on the display panel while an image is being displayed on the display panel in a normal operating phase of the display panel.
 15. A display apparatus comprising: a display panel; a backlight configured to illuminate the display panel from the rear; a sensor configured to measure a luminance, and arranged, in a standby position, in an area that is not visible to a viewer; a backlight control configured to adjust the intensity of the backlight to a setpoint value based on the luminance measured by the sensor; a swivel configured to swivel the sensor, during a calibration phase and substantially parallel to the display panel, from the standby position to a measurement position, to measure the luminance of a test image that is displayed on the display panel.
 16. A display apparatus as claimed in claim 15, wherein the swivel is configured to lower the sensor toward the display panel when the sensor is swiveled out.
 17. A display apparatus as claimed in claim 15, further comprising a shield configured to shield the sensor from ambient light while the luminance is measured.
 18. A display apparatus as claimed in claim 17, wherein the shield comprises sealing lips.
 19. A display apparatus as claimed in claim 15, further comprising a cleaner configured to clean the sensor while the sensor is swiveled out into the measurement position.
 20. A display apparatus as claimed in claim 15, wherein the sensor and the swivel are arranged in a recess of a frame of the display panel.
 21. A display apparatus as claimed in claim 15, further comprising a cleaner configured to clean the sensor while the sensor is swiveled back into it the standby position.
 22. A display apparatus as claimed in claim 15, wherein the test image is displayed in a window on the display panel which is smaller in size than the display panel.
 23. A display apparatus as claimed in claim 15, wherein the test image is displayed in a window on the display panel while an image is being displayed on the display panel in a normal operating phase of the display panel. 